Internal combustion engines are known which utilize spark-ignited direct in-cylinder fuel injection systems. The fuel injection mechanisms spray a fuel mist directly into each cylinder and inlet air is directed into the cylinder from one or more inlet ports to produce an appropriate air-fuel mixture in the combustion chamber. The air-fuel mixture is ignited by a spark plug during each cycle of the piston in the cylinder bore. Various piston bowl and combustion chamber configurations have been devised in order to provide appropriate air-fuel mixing and to direct the mixtures toward the spark plug for ignition, particularly in low load operation of the engines. It is an object of these systems to provide an overall lean but ignitable gas mixture and to reduce undesirable emissions in order to meet appropriate standards of fuel economy and emissions.
One object of these systems is to achieve charge stratification through direct fuel injection into the combustion chamber with minimum wall wetting by the fuel and with an overall lean but locally burnable fuel-air mixture directed to the spark plug.
Several attempts have been made to accomplish this by reorganizing the combustion chamber configuration, modifying the in-cylinder air flow, and optimizing fuel injection with respect to timing, location and spray characteristics. For example, U.S. Pat. No. 5,711,269 discusses a reverse tumble combustion system with a spherical bowl in the top of the piston near the intake valve side and with a fuel injector in the intake valve side. Also, U.S. Pat. No. 5,259,348 shows a stratified-charge combustion system with a swirl air flow and a bowl in the piston at the intake valve side. Although these systems have appeared to work well in practice, they still have relatively high hydrocarbon emissions and soot formation, some of which may result from an undesirable amount of wetting of the piston wall by the fuel spray.
It is thus desirable to provide a combustion chamber design which minimizes wetting of the piston bowl wall by the fuel injector and which further reduces hydrocarbon emissions and soot formation.